Work pieces such as strips or sheets including an aluminum alloy are often surface treated after finishing rolling to prepare them for the next manufacturing step. In particular strips or sheet for lithographic printing are conditioned to achieve a predetermined surface roughness in a subsequent graining process. Lithostrips or sheets are usually degreased after finishing rolling. As known from the US-patent specification U.S. Pat. No. 5,997,721, degreasing respectively cleaning of the surface is done in one step by anodising the aluminum alloy sheet with AC current in an acidic electrolyte bath. Another way to degrease or clean aluminum slivers is known from the German patent DE 43 17 815 C1 namely the use of an alkaline medium.
Prior to electro-chemical graining of the lithostrips, they can be subjected to sodium hydroxide in a pre-treatment to degrease and clean the surface again. This step takes place in principle at the side of the manufacture of lithographic printing plates. Due to the increasing manufacturing speed during electro-chemical graining of the lithostrips time for pre-treatment of the surface of the lithostrips and for the electro-chemical graining itself decreases. Due to the increasing manufacturing speed the pre-treatment with sodium hydroxide is not sufficient enough to remove all contaminants from the surface of the lithostrip. As a consequence, the results in electro-chemically graining are not stable and surface defects occur on electro-chemically grained lithostrips or sheets. A reduction of the manufacturing speed causes higher production costs for lithographic printing plates.